CN112111033A - Carbon dioxide viscosity-increasing and fluid loss-reducing copolymer and preparation method and application thereof - Google Patents
Carbon dioxide viscosity-increasing and fluid loss-reducing copolymer and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer as well as a preparation method and application thereof. The carbon dioxide viscosity-increasing and fluid loss-reducing copolymer comprises a structural unit A with a structure shown in a formula I, a structural unit B with a structure shown in a formula II and a structural unit C with a structure shown in a formula III;
the invention also provides a preparation method of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer and application of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer as a viscosity-increasing and fluid loss-reducing agent in carbon dioxide. The carbon dioxide viscosity-increasing and fluid loss-reducing copolymer provided by the invention can improve the suspension and carrying capacity of carbon dioxide serving as drilling fluid and fracturing fluid on rock debris and propping agent, adjust rheological property, improve the viscosity of a system, reduce the fluid loss of carbon dioxide in a reservoir and improve the displacement efficiency of carbon dioxide serving as displacement fluid.
Description
Technical Field
The invention relates to the technical field of unconventional oil and gas development in the petroleum industry. More particularly, relates to a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer, and a preparation method and application thereof.
Background
The external dependence of petroleum in China exceeds 50%, and the development of shale gas resources has a great significance on energy safety in China. Due to the differences of geological characteristics of shale gas reservoirs, surface conditions and the like, the existing shale gas development technology in foreign countries cannot be completely adapted to the situation of China. According to the characteristics of the shale gas reservoir in China, the anhydrous fracturing technology is a development direction for realizing the efficient development of shale gas.
The carbon dioxide is expected to replace a traditional green solvent, and has high application potential in shale gas development. The carbon dioxide jet drilling can obtain higher mechanical drilling speed in the shale layer, and the shale layer cannot generate the effects of clay expansion, water lock and the like. The carbon dioxide fluid is used for carrying out reservoir fracturing transformation, so that more micro cracks can be generated in the reservoir, and the shale gas production is facilitated. The adsorption strength of the carbon dioxide and the shale is higher than that of methane, the methane adsorbed on the shale can be replaced, and the shale gas recovery rate can be improved. In carbon dioxide drilling, cuttings produced downhole need to be carried to the surface by the carbon dioxide. In carbon dioxide sand fracturing, carbon dioxide is not only used to fracture the reservoir to create fractures, but also to transport it as deep as possible into the fractures as a carrier for the proppant.
But SC-CO2The viscosity is low, the sand and rock carrying effects are poor, the difference of the fluidity of the oil and the sand and rock carrying effect is large, and the oil recovery efficiency is low and the fingering phenomenon is obvious for improving the oil recovery efficiency. The most direct approach to this problem is to SC-CO2The viscosity of carbon dioxide is effectively improved by adding the viscosity-increasing fluid loss additive by adding the chemical tackifier, so that CO can be effectively controlled2The fingering phenomenon of (1) improves the economy of EOR, can also improve the rock-carrying efficiency in well drilling, spreads wider cracks in fracturing, carries larger proppant particles into the cracks, and reduces CO on the crack surface2And (4) fluid loss.
The carbon dioxide adhesion promoter should also be provided in the presence of CO2The dissolving property and the viscosity-improving property of the composition. At present, the research on carbon dioxide tackifiers at home and abroad is still in an exploration stage, the tackifying performance of the small molecular tackifiers is weak, and the shearing resistance of the system is poor. The vast majority of polymers are in CO2Has poor dissolving property in CO2The polymer (A) does not necessarily have good thickening properties.
Therefore, the invention provides a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer, a preparation method and application thereof, which aim to solve the problems.
Disclosure of Invention
It is a first object of the present invention to provide a carbon dioxide fluid loss viscosity increasing copolymer; the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer has good solubility in carbon dioxide and viscosity-increasing and fluid loss-reducing effects, and solves the problems of low viscosity, serious fluid loss, poor sand carrying and displacement effects of carbon dioxide.
The second purpose of the invention is to provide a preparation method of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer.
The third purpose of the invention is to provide the application of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer.
In order to achieve the purpose, the invention adopts the following technical scheme:
a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer comprises a structural unit A with a structure shown in a formula I, a structural unit B with a structure shown in a formula II and a structural unit C with a structure shown in a formula III;
in the formula I, the formula II and the formula III,
R1、R3、R5、R6and R7Each independently represents H or an alkyl group having from C1 to C8,
R2a fluorocarbon group represented by C1 to C8,
R4represents a single bond or an alkylene group having C1 to C8.
Preferably, R1、R3、R5、R6And R7Each independently represents H or C1-C7 alkyl, R2C3-C8 fluorocarbon group, R4Represents a single bond or an alkylene group having C1 to C6.
Preferably, R1、R3、R5And R6Each independently represents H or C1-C4 alkyl, R2C4-C8 fluorocarbon group, R4Represents a single bond or an alkylene group having C1 to C4, R7Represents a C1-C7 alkyl group.
Preferably, R1、R3、R5And R6Each independently represents H, methyl, ethyl, n-propyl, isopropyl or n-butyl; r4Represents a single bond or a methylene group; r7Is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, n-heptyl or n-octyl.
Preferably, the weight average molecular weight of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer is 150000-500000 g/mol; further, the weight average molecular weight of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer is 200000-400000 g/mol; more preferably, the weight average molecular weight of the carbon dioxide viscosity increasing and fluid loss reducing copolymer is 250000-350000 g/mol.
Preferably, the molar ratio of the structural unit A to the structural unit B to the structural unit C is 15-60: 10-35: 10-60; further, the molar ratio of the structural unit A to the structural unit B to the structural unit C is 25-35: 20-30: 40-60.
The invention also provides a preparation method of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer, which comprises the following steps:
in the presence of a free radical initiator, carrying out free radical polymerization reaction on a compound D with a structure shown in a formula I ', a compound E with a structure shown in a formula II ' and a compound F with a structure shown in a formula III ' to obtain a carbon dioxide fluid loss copolymer for improving viscosity and reducing fluid loss; wherein the content of the first and second substances,
in the formulae I ', II ' and III ', R1、R2、R3、R5、R6And R7As previously defined, are not described in detail herein.
Preferably, the molar ratio of the compound D to the compound E to the compound F is 15-60: 10-35: 10-60; further, the molar ratio of the compound D to the compound E to the compound F is 25-35: 20-30: 40-60.
Preferably, the free radical initiator is one or more of azobisisobutyronitrile, 4' azo (4-cyanovaleric acid), azobisisobutylamidine hydrochloride, azobisisopropylimidazoline hydrochloride, and azobisisobutylimidazoline hydrochloride.
Preferably, the amount of the radical initiator is 0.07 to 0.25mmol, more preferably 0.11 to 0.18mmol, based on 1mol of the total amount of the compound D, the compound E and the compound F.
Preferably, the conditions of the radical polymerization reaction include: under the protection of inert gas, the temperature of free radical polymerization is 50-70 ℃, and the time of free radical polymerization is 6-36 h.
Preferably, the conditions of the radical polymerization reaction include: under the protection of inert gas, the temperature of free radical polymerization is 55-65 ℃, and the time of free radical polymerization is 20-30 h.
Preferably, the inert gas comprises at least one of nitrogen or a gas of an element of group zero of the periodic table of the elements, which is conventional in the art, and more preferably nitrogen.
Preferably, the preparation method of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer specifically comprises the following steps: firstly, mixing a compound D with a structure shown in a formula I ', a compound E with a structure shown in a formula II ' and a compound F with a structure shown in a formula III ', adding a free radical initiator, and carrying out free radical polymerization reaction under an inert gas atmosphere to obtain the carbon dioxide adhesion-improving and fluid loss-reducing copolymer. The method can better control the progress of the free radical polymerization reaction.
Preferably, the free radical polymerization reaction is followed by a step of vacuum drying the resulting product, thereby extracting the carbon dioxide viscosifying fluid loss copolymer from the free radical polymerization reaction product.
The invention also provides the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer prepared by the preparation method.
The invention also provides the application of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer or the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer prepared by the preparation method in carbon dioxide as a viscosity-increasing and fluid loss-reducing agent.
The invention also provides the viscosity increasing and fluid loss reducing effects of the carbon dioxide viscosity increasing and fluid loss reducing copolymer in carbon dioxide.
The invention also provides a carbon dioxide drilling fluid, a fracturing fluid and a displacement fluid which use the carbon dioxide viscosity-increasing and fluid-loss-reducing copolymer or the carbon dioxide viscosity-increasing and fluid-loss-reducing copolymer prepared by the method as a viscosity-increasing and fluid-loss-reducing agent.
The invention also provides application of the carbon dioxide drilling fluid, the fracturing fluid and the displacement fluid in oil and gas drilling, oil and gas reservoir transformation and oil and gas displacement respectively.
In addition, unless otherwise specified, any range recited herein includes any value between the endpoints and any sub-range defined by any value between the endpoints or any value between the endpoints.
The invention has the following beneficial effects:
the invention provides the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer with good solubility, viscosity-increasing and fluid loss-reducing effects in carbon dioxide aiming at the defects of low viscosity, serious fluid loss, sand carrying and poor displacement effect of carbon dioxide, can improve the suspension and carrying capacity of the carbon dioxide serving as drilling fluid and fracturing fluid on rock debris and propping agent, adjust rheological property, improve the viscosity of a system, reduce the fluid loss of the carbon dioxide in a reservoir and improve the displacement efficiency of the carbon dioxide serving as a displacement fluid.
Drawings
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
FIG. 1 shows CO at 35 ℃ under 30MPa in example 1 of the present invention2The phase of the viscosity enhancer system is plotted as a function of viscosity with mass concentration of carbon dioxide viscosity enhancing fluid loss copolymer a 1.
FIG. 2 shows CO at 35 ℃ under 30MPa in example 2 of the present invention2The phase of the viscosity enhancer system is plotted as a function of viscosity with mass concentration of carbon dioxide viscosity enhancing fluid loss copolymer a 2.
Detailed Description
In order to more clearly illustrate the invention, the invention is further described below in connection with preferred embodiments. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention.
In the invention, the preparation method is a conventional method if no special description is provided; the starting materials used are commercially available from published sources unless otherwise specified.
The invention provides a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer which comprises a structural unit A with a structure shown in a formula I, a structural unit B with a structure shown in a formula II and a structural unit C with a structure shown in a formula III;
in the formula I, the formula II and the formula III,
R1、R3、R5、R6and R7Each independently represents H or a C1-C8 alkyl group, and the C1-C8 alkyl group may be, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, an n-heptyl group, an n-nonyl group, or the like.
R2A fluorocarbon group represented by C1 to C8,
R4represents a single bond or an alkylene group having from C1 to C8, wherein the single bond may be considered to be R4The groups at both ends are directly connected.
The carbon dioxide viscosity-increasing and fluid loss-reducing copolymer can fully expand molecular chains in carbon dioxide, is mixed with the carbon dioxide to form a single phase, and forms a spatial network structure through intermolecular association and intermolecular mutual winding, so that the viscosity of the carbon dioxide is greatly improved, and the fluid loss of the carbon dioxide in a reservoir stratum is reduced.
In order to be able to better exert the effect of the copolymer as a viscosity enhancer, R is a preferred embodiment of the present invention1、R3、R5、R6And R7Each independently represents H or C1-C7 alkyl, R2C3-C8 fluorocarbon group, R4Represents a single bond or an alkylene group having C1 to C6.
More preferably, R1、R3、R5And R6Each independently represents H or C1-C4 alkyl, R2C4-C8 fluorocarbon group, R4Represents a single bond or an alkylene group having C1 to C4, R7Represents a C1-C7 alkyl group.
More preferably, R1、R3、R5And R6Each independently represents H, methyl, ethyl, n-propyl, isopropyl or n-butyl; r4Represents a single bond or a methylene group; r7Is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, n-heptyl or n-octyl.
According to the invention, the weight average molecular weight of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer is preferably 150000-500000 g/mol, preferably 200000-400000 g/mol, and more preferably 250000-350000 g/mol. When the weight average molecular weight of the carbon dioxide viscosity-increasing fluid loss copolymer is within the range, particularly 250000-350000 g/mol, the obtained carbon dioxide viscosity-increasing fluid loss copolymer can be better used as a viscosity-increasing fluid loss agent, and can keep better performance in carbon dioxide.
According to the present invention, although the amount of the structural unit a having the structure represented by formula I, the structural unit B having the structure represented by formula II and the structural unit C having the structure represented by formula III contained in the carbon dioxide fluid loss increasing and reducing copolymer can vary within a wide range, in view of optimizing the fluid loss increasing and reducing performance of the resulting carbon dioxide fluid loss increasing and reducing copolymer, it is preferable that the molar ratio of the structural unit a, the structural unit B and the structural unit C is 20 to 70: 10-40: 20-70, preferably 20-30: 30-40: 30 to 70, preferably 25 to 30: 35-40: 30-40.
The carbon dioxide fluid loss adhesion-promoting copolymer of the present invention may comprise other structural units which do not affect its performance as an adhesion-promoting fluid loss additive, and the terminal group thereof is not particularly limited, and is typically hydrogen.
The invention also provides a preparation method of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer, which comprises the following steps:
in the presence of a free radical initiator, carrying out free radical polymerization reaction on a compound D with a structure shown in a formula I ', a compound E with a structure shown in a formula II ' and a compound F with a structure shown in a formula III ' to obtain a carbon dioxide fluid loss copolymer for improving viscosity and reducing fluid loss; wherein the content of the first and second substances,
in the formulae I ', II ' and III ', R1、R3、R5、R6And R7Each independently represents H and/or C1-C8 alkyl, R2C1-C8 fluorocarbon group, R4Represents a single bond or an alkylene group having C1 to C8.
R in the above1、R2、R3、R5、R6And R7As described above, no further description is provided herein. The compound D having the structure represented by formula I ', the compound E having the structure represented by formula II ', and the compound F having the structure represented by formula III ' may also be appropriately selected according to the kinds of the specific structural unit a, structural unit B, and structural unit C of the carbon dioxide fluid loss and viscosity improving copolymer described hereinabove.
The amount of the monomer compound may be selected depending on the ratio of the structural units of the desired copolymer and the molecular weight, and as a preferred embodiment of the present invention, the molar ratio of the compound D, the compound E and the compound F is 15 to 60: 10-35: 10-60, preferably 25-35: 20-30: 40-60.
The radical polymerization reaction may be initiated using various radical initiators conventionally used in the art, but in view of reactivity among the above-mentioned monomers, the radical initiator is one or more of azobisisobutyronitrile, 4' -azo (4-cyanovaleric acid), azobisisobutylamidine hydrochloride, azobisdiisopropylimidazoline hydrochloride, and azobisisobutylimidazoline hydrochloride, as a preferred embodiment of the present invention. The amount of the radical initiator can vary within wide limits, and is preferably from 0.07 to 0.25mmol, preferably from 0.11 to 0.18mmol, based on 1mol of the total of the compound D, the compound E and the compound F.
In order to be able to maintain the activity of the radical initiator and the like, the method may further include, as a preferred embodiment of the present invention: the radical polymerization is carried out in an inert atmosphere, for example, one or more of nitrogen, helium, neon, argon and the like may be introduced into the system and the air therein may be replaced.
In a preferred embodiment of the present invention, the temperature of the radical polymerization reaction is 50 to 70 ℃, and the time of the radical polymerization reaction is 6 to 36 hours; further preferably, the temperature of the free radical polymerization reaction is 55-65 ℃, and the time of the free radical polymerization reaction is 20-30 h.
In order to better control the proceeding of the above free radical polymerization reaction, as a preferred embodiment of the present invention, the preparation method of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer specifically comprises the following steps: mixing a compound D with a structure shown in a formula I ', a compound E with a structure shown in a formula II ' and a compound F with a structure shown in a formula III ', adding a free radical initiator, and carrying out free radical polymerization reaction under an inert gas atmosphere (for example, one or more of nitrogen, helium, neon and argon can be introduced into the system, and air in the system can be replaced), thereby obtaining the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer.
In accordance with the present invention, to enable extraction of the carbon dioxide viscosifying fluid loss copolymer from the product of the free radical polymerization reaction, the method may further comprise: and (3) drying the product of the free radical polymerization reaction in vacuum to obtain the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer.
The invention also provides the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer prepared by the preparation method. Although the present invention is not particularly limited, the carbon dioxide viscosifying fluid loss copolymer may be considered one of the carbon dioxide viscosifying fluid loss copolymers described above, or a mixture of a plurality of carbon dioxide viscosifying fluid loss copolymers. It should be understood, of course, that the carbon dioxide viscosifying fluid loss copolymers produced by the above-described processes are generally the direct product of the above-described processes without purification (or after just vacuum drying as described above), and that while such products may be a mixture of polymers, the present invention also includes such cases within the scope of the present invention.
The invention also provides the application of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer or the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer prepared by the preparation method in carbon dioxide as a viscosity-increasing and fluid loss-reducing agent.
The invention also provides the viscosity increasing and fluid loss reducing effects of the carbon dioxide viscosity increasing and fluid loss reducing copolymer in carbon dioxide.
The invention also provides a carbon dioxide drilling fluid, a fracturing fluid and a displacement fluid which use the carbon dioxide viscosity-increasing and fluid-loss-reducing copolymer or the carbon dioxide viscosity-increasing and fluid-loss-reducing copolymer prepared by the method as a viscosity-increasing and fluid-loss-reducing agent.
The invention also provides application of the carbon dioxide drilling fluid, the fracturing fluid and the displacement fluid in oil and gas drilling, oil and gas reservoir transformation and oil and gas displacement respectively.
The present invention will be further described with reference to the following examples.
Example 1
The embodiment provides a preparation method of a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer A1, which comprises the following steps:
mixing 3,3,4,4,5,5,6,6,7,8,8, 8-dodecafluoro-7- (trifluoromethyl) octyl acrylate, vinyl pivalate and allyl benzene (in a molar ratio of 3: 4: 3) in a polymerization tube, and adding azobisisobutyronitrile as a radical initiator thereto; after three times of freeze-thaw cycle to completely remove oxygen, decompressing and sealing the polymerization tube, and reacting for 24 hours at 60 ℃; dissolving the reaction product in 1,1, 2-trichlorotrifluoroethane, precipitating twice in methanol for purification, and vacuum drying the reaction product collected after filtration to obtain the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer A1.
The weight average molecular weight of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer A1 is 180000g/mol, the molecular weight distribution coefficient is 1.21, and the molar ratio of a structural unit A with a structure shown in a formula I, a structural unit B with a structure shown in a formula II and a structural unit C with a structure shown in a formula III is 3 through infrared and nuclear magnetic resonance hydrogen spectrum and carbon spectrum analysis and detection: 3.75: 3.1.
this example also provides a method of measuring the viscosity increasing and fluid loss effect of carbon dioxide viscosity increasing and fluid loss copolymer a1, comprising the steps of:
carbon dioxide and the carbon dioxide fluid loss additive A1 prepared in this example were added to a high-pressure viscosity measurement experimental apparatus, and the viscosity increasing effect of the adhesive was measured by a falling ball method. Introducing CO2Viscosity number of the adhesion promoter System with pure CO measured under the same conditions of temperature and pressure2The viscosity values of (A) and (B) are compared, and the ratio, namely the viscosity-increasing factor, is used for evaluating the viscosity-increasing performance of the viscosity-increasing agent, wherein the larger the viscosity-increasing factor is, the better the viscosity-increasing performance is. As can be seen from fig. 1, the carbon dioxide fluid loss viscosity increasing and reducing copolymer a1 of the present invention shows a significant viscosity increasing effect in carbon dioxide, which effectively increases the viscosity of carbon dioxide.
Example 2
The embodiment provides a preparation method of a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer A2, which comprises the following steps:
mixing 3,3,4,4,5,5,6,6,7,8,8, 8-dodecafluoro-7- (trifluoromethyl) octyl acrylate, vinyl pivalate and allyl benzene (molar ratio 4: 4: 2) in a polymerization tube, and adding azobisisobutyronitrile as a radical initiator thereto; after three times of freeze-thaw cycle to completely remove oxygen, decompressing and sealing the polymerization tube, and reacting for 24 hours at 60 ℃; dissolving the reaction product in 1,1, 2-trichlorotrifluoroethane, precipitating twice in methanol for purification, and vacuum drying the reaction product collected after filtration to obtain the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer A2.
The weight average molecular weight of the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer A2 is 190000g/mol, the molecular weight distribution coefficient is 1.30, and the molar ratio of a structural unit A with a structure shown in a formula I, a structural unit B with a structure shown in a formula II and a structural unit C with a structure shown in a formula III is 4 through infrared and nuclear magnetic resonance hydrogen spectrum and carbon spectrum analysis and detection: 4.1: 2.2.
the present example also provides a method for measuring the viscosity increasing effect of carbon dioxide viscosity increasing fluid loss copolymer a2, comprising the steps of:
carbon dioxide and the carbon dioxide fluid loss additive A2 prepared in this example were added to a high-pressure viscosity measurement experimental apparatus, and the viscosity increasing effect of the adhesive was measured by a falling ball method. As can be seen from FIG. 2, the carbon dioxide viscosity increasing and fluid loss reducing copolymer A2 of the present invention shows a significant viscosity increasing effect in carbon dioxide, which effectively increases the viscosity of carbon dioxide.
It should be understood that the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention, and it will be obvious to those skilled in the art that other variations or modifications may be made on the basis of the above description, and all embodiments may not be exhaustive, and all obvious variations or modifications may be included within the scope of the present invention.
Claims (10)
1. A carbon dioxide viscosity increasing and fluid loss reducing copolymer is characterized by comprising a structural unit A with a structure shown in a formula I, a structural unit B with a structure shown in a formula II and a structural unit C with a structure shown in a formula III;
in the formula I, the formula II and the formula III,
R1、R3、R5、R6and R7Each independently represents H or an alkyl group having from C1 to C8,
R2a fluorocarbon group represented by C1 to C8,
R4a single bond or an alkylene group having C1 to C8;
the molar ratio of the structural unit A to the structural unit B to the structural unit C is 15-60: 10-35: 10 to 60.
2. The carbon dioxide viscosifying fluid loss copolymer of claim 1, wherein the weight average molecular weight of the carbon dioxide viscosifying fluid loss copolymer is 100000-600000 g/mol.
3. The carbon dioxide adhesion promoting and fluid loss reducing copolymer of claim 1, wherein the molar ratio of the structural unit A, the structural unit B and the structural unit C is 25-35: 20-30: 40-60.
4. A preparation method of a carbon dioxide viscosity-increasing and fluid loss-reducing copolymer is characterized by comprising the following steps: in the presence of a free radical initiator, carrying out free radical polymerization reaction on a compound D with a structure shown in a formula I ', a compound E with a structure shown in a formula II ' and a compound F with a structure shown in a formula III ' to obtain a carbon dioxide fluid loss copolymer for improving viscosity and reducing fluid loss; wherein the content of the first and second substances,
in the formulae I ', II ' and III ', R1、R3、R5、R6And R7Each independently represents H or C1-C8 alkyl, R2C1-C8 fluorocarbon group, R4Represents a single bond or an alkylene group having C1 to C8.
5. The method for preparing the carbon dioxide viscosity-increasing and fluid loss-reducing copolymer according to claim 4, wherein the molar ratio of the compound D to the compound E to the compound F is 15-60: 10-35: 10 to 60.
6. The method of claim 4, wherein the free radical initiator is one or more of azobisisobutyronitrile, 4' -azo (4-cyanovaleric acid), azobisisobutylamidine hydrochloride, azobisdiisopropylimidazoline hydrochloride, and azobisisobutylimidazoline hydrochloride.
7. The method for preparing the carbon dioxide viscidity-improving and fluid loss-reducing copolymer according to claim 4, wherein the amount of the free radical initiator is 0.07-0.25 mmol based on 1mol of the total amount of the compound D, the compound E and the compound F.
8. The method of claim 4, wherein the free radical polymerization conditions comprise: under the protection of inert gas, the temperature of free radical polymerization is 50-70 ℃, and the time of free radical polymerization is 6-36 h.
9. A carbon dioxide viscosity increasing and fluid loss reducing copolymer prepared by the preparation method of any one of claims 4 to 8.
10. Use of a carbon dioxide adhesion promoting fluid loss copolymer according to any one of claims 1 to 3 and 9 as an adhesion promoting fluid loss agent in carbon dioxide.
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